Pro Stock Mountain Motors have cubic inch displacements of 820 to 825. Their capacities began much smaller, deriving from original equipment big-block engines of the ‘60s. But gradually the dimensions between their pan rails grew, allowing longer throw cranks to appear with connecting rods measuring 7.750 inches center to center and 5-inch bore centers with 4.770-inch-diameter pistons, all functioning within a deck height of 12 inches. Today’s Pro Stock engines operate on compression ratios of around 18:1, run on VP Race Fuel grade Q16, and generate in the region of 1,900 hp. Depending on weather conditions, they run quarter-mile elapsed times in 6.25 seconds at speeds close to 225 mph.
Jon Kaase Racing Engines has been a driving force in the development of these engines for as long as most can remember. From the beginning, when he worked with Dyno Don Nicholson, Kaase imposed uncompromising standards in race engine building. And his record of success has been impressive: He and his team have produced Pro Stock engines for 12 IHRA national championship winners, plus an NHRA Pro Stock title. Though their business now includes engine part sales to hot rodders, including the supply of the remarkable Boss Nine engine, the Winder, Georgia, firm still maintains about 20 Mountain Motor customers, refurbishing these formidable power plants after every 25 to 30 runs.
When reciprocating engine parts collide (usually pistons and valves) and a connecting rod or rods explode through the engine walls or the oil pan or both, foreign particles are immediately released into the oil stream to be sucked into the oil pump rotors. Rod bearings are often first to disintegrate, showering the pump with brass, copper and aluminum. Seasoned start-line observers will regale you with stories of inexperienced drivers breaking connecting rods at the starting lights and driving the entire length of the track, unaware that the vibration from the engine compartment was a signal of terminal distress. If the camshaft can still operate, usually the engine will continue to keep running—tearing itself apart all the way!
The chief concern about engine durability is the limited life of the connecting rods and also the condition of the skinny top pistons rings. The life cycle of these critical parts and others must be strictly observed in the rarified air of Mountain Motor Pro Stock racing.
In Kaase’s dynamometer cell, before this engine was tested, ace builder Chuck Lawrence leaned across to a visitor and said, “Have you ever heard one of these on a dyno before?” The visitor shook his head. “It’s pretty cool,” Lawrence insisted, “I never get tired of it.” He was right: that sound resides indelibly in the memory. Captured in the following images is the rebuilding process of a Mountain Motor Pro Stock engine.
Text and Photos by Sam Moore
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| DR-1101-KAASE-LEAD |
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| The engine is dismantled and the crankshaft is removed, cleaned and
Magnaflux tested (a non-destructive fluorescent dye penetrant that
reveals the location of surface and subsurface flaws). |
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| New Mountain Motor engine blocks are available in either cast
form from C&C Motorsports or in billet form from Dart. Here the
billet block is exposed to the cleaning process |
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| The art of cylinder honing is never taken more seriously than at
Kaase’s. It is the key to gaining an edge on power output while
maintaining a fine, consistent pattern of cross hatch scratches that
lubricate the rings. |
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| Piston pins are checked for straightness, and run-out is measured to
0.0001-inch (a tenth of one thousand inch). The run-out on the average
pin is usually around this figure; if the indicator shows run-out of
0.0005-inch (five tenths of a thousand inch) the pin will be renewed. |
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| Until five years ago Kaase used titanium connecting rods. Today they
have been replaced mainly by aluminum. Shown on the left is an example
of a titanium connection rod and on the right is the aluminum
counterpart. The Diamond Pro Stock piston features inboard pin bosses,
stiffening ribs, shorter pins and minimal skirts to decrease frictional
loses. Friction is further reduced by the use of thin .8mm top rings and
Napier-style second rings. Trend’s piston pins are coated in a
diamond-like carbon and retained in the piston with single round wire
locks. |
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The mighty Bryant billet crankshaft resides in the aluminum block and
functions with aluminum rods, aluminum bearing caps and aluminum main
caps. Aluminum is lighter than steel, and it also makes accurate line
boring easier. When honing dissimilar metals (an alloy block with steel
caps), the hone is inclined to push toward the softer metal.
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The
diameter of the forged pistons usually measures 4.770 inches. The
small-bore holes around the perimeter of the CP pistons are gas ports.
These allow combustion gases to enter the top ring grooves, imposing a
force on the inner edge of the top rings and forcing them out onto the
cylinder walls.
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This five-stage oil pump (four scavenge, one pressure) has
fine mesh screens embedded in the fittings at the ends of the number 12
lines to minimize the risk of particles entering the pump. But in the
aftermath of a blow-up, fine debris usually penetrates to the heart of
the system, and the lines and pump parts have to be cleaned and the
rotors buffed smooth if necessary. Each of the four scavenge pumps
conveys oil from assigned areas of the oil pan and transports it into
the oil reservoir. The pressure pump (the one at the end) pumps oil from
the bottom of the reservoir and into the filter. From the filter it is
transported into the block.
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The first part of the process of installing the valves is to
check the continuity of the seal between the valve head and the valve
seat. This is accomplished by applying red dye to the seats and lapping
the valves into them. If continuity is broken and traces of red dye
remain, the offending seats will be recut. Both inlet and exhaust valves
are made of titanium. The diameter of the inlet valve measures 2.680
inches and the exhaust measures 2.040 inches.
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| Next, the tension of the triple valve springs is checked. Though the
desired seat pressure and the installed height measurement change with
different camshaft designs, Kaase’s most regular combination generates
around 475 pounds at an installed height of 2.400 inches. Both inlet and
exhaust valves, as well as the retainers, are made of titanium.
Installed heights are maintained within 0.005-inch to 0.010-ichn by
adding shims under the springs. Trend Performance provides shims in
increments of 0.015, 0.030 or 0.060-inch. |
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Next, the triple valve springs are laid out for installation.
Hardened seats are fitted between the spring and the aluminum head. Oil
is applied to the valve stems and the valves are inserted into the
cylinder head. Aided by a pneumatic valve spring compressor, the locks
are carefully sandwiched between the valve stems and the retainers.
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Copper spray from an aerosol can is applied to the top and bottom
surfaces of the three-layer Cometic head gaskets, then the heads are
fitted and tensioned to 130-140 ft-lb.
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Pushrods are installed, WW billet rockers positioned, their
shafts tightened to 35 ft -b and valve lash adjusted for engine warming
on the dyno. Usually the clearance between the exhaust valve and the
rocker is zero, and the clearance between the inlet valve and the rocker
is 1/8th of a turn from tight. In this way, when the engine warms the
inlet valve lash will measure 0.030-inch and the exhaust 0.020-inch.
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| With gaskets glued to the flanges, the intake manifold and carburetors are set in position |
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Curiously, the power of the vacuum pump can deflect the top
skin of the alloy valve covers enough to propagate a crack around the
plug holes. Welding the crack is not without its troubles. Invariably
another crack will develop beside the weld.
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The best solution for sealing the crack around the plug hole
is to apply a special silicone sealer, the cost of which is around $80
for a small tube.
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A vacuum pump can generate in excess of 22 inches of vacuum
and is so effective it liberates 25 to 30 extra hp. It has the ability
to improve ring seal and efficiently evacuates the turbulent air and oil
mist from the under the reciprocating pistons in the crankcase, the
valley area under the intake manifold, and the valve gear chambers on
top of the cylinder heads. It often discharges to a canister through a
port in the valley (under the intake plenum) or from the front face of
the right cylinder head.
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The effects of even the most powerful dyno-room fans are far
removed from the pressurized air traveling through a hood scoop of a Pro
Stock race car at 200 mph. Still, the dynamometer plays a vital role in
assessing the engine’s condition: It allows for the examination of
engine vacuum and oil pressure, of oil or water leaks, and it allows one
to learn how the engine runs and whether it performs as expected. Jon
Kaase’s notability rests not only on his gift for making big power, but
also in his commitment to his customers—he presides over every test
Posted BY Drag Racer |
